Pangea Heats Up: Wide Extension & the NW European Triassic
Department of Geology, University College Dublin, Ireland
The hypothesis of supercontinental episodicity proposes that the Mesozoic break-up of Pangea was driven by thermal upwelling in response to insulation of the mantle, resulting in extension from sometime in the Triassic. In NW Europe, Triassic basins extend across remarkably wide areas (100s-1000s kms) and the tectonic controls on their formation have long been problematic. Theoretical analyses of intracratonic extension show that wide extension may take place where unthickened lithosphere is persistently warmed, through mechanisms of strain delocalisation that include multiple boudinage (shifting loci of strain). The boudinage mechanism is consistent with a new tectonostratigraphic model for the NW European Triassic, in which Early Triassic regional regression (and expansion of long-distance drainage systems) gave way, across the continent-wide Hardegsen discordance (ca. 243 Ma), to episodic low-magnitude (beta < 1.2) wide extension (and drainage internal to widely distributed fault-bound depocentres that shifted over time). The regional regression is interpreted to record dynamic topographic uplift in response to mantle upwelling, followed by wide extension to form “boudinage basins” within the heated lithosphere. Boudinage gave way to localised Atlantic-style rifting in the Jurassic as the lithosphere (and mantle) cooled. Transitions from wide to narrow extension are expected Pangea-wide, if this interpretation is correct.